From mboxrd@z Thu Jan 1 00:00:00 1970 From: Balaji Rao Subject: Re: Performance monitoring units and KVM Date: Thu, 31 Jan 2008 00:25:44 +0530 Message-ID: <200801310025.44957.balajirrao@gmail.com> References: <87wsprxmyb.fsf@pike.pond.sub.org> <200801302353.19872.balajirrao@gmail.com> <47A0BE8F.4090508@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Markus Armbruster To: Avi Kivity Return-path: In-Reply-To: <47A0BE8F.4090508-atKUWr5tajBWk0Htik3J/w@public.gmane.org> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Wednesday 30 January 2008 11:44:39 pm Avi Kivity wrote: > Balaji Rao wrote: > > But don't the architectural performance counters vary between Intel and > > AMD cpus ? AFAIK, they do. And, this would pose problems during migration > > between Intel and AMD hosts. > > The also vary between Intel hosts of different models, and likely > different AMD hosts as well. The PMU is not architectural (or, in other > words, model specific). So migration and PMU pass-through are mutually > exclusive unless you have a homogeneous server farm. > Right. I had confused myself in understanding that Architectural Performance monitoring is consistent across all processors right from P6. But infact it was introduced starting with core solo and core duo. > > I am not sure how important is it to support migration between Intel and > > AMD hosts. If it were not that important, then IMO we could go ahead with > > exposing the real PMU. Maybe we could warn users against running > > profilers in the guest if they intend it to to be Intel<->AMD migrateable > > ? > > We can give the user the option to expose only the architectural PMU > (which is quite limited) and have cross-model migration, or to expose > the full PMU and lose hardware independence. Yes. This looks like the right thing to do.. regards, balaji rao ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/